JPH03182875A - Protection device for motor in electrically driven power steering device - Google Patents

Abstract

PURPOSE:To surely detect the ground of an assist motor at the hot side by extracting terminal voltage at the hot side in response to polarity out of terminal voltages at the both sides of the assist motor, and thereby comparing the extracted terminal voltage with a specified threshold voltage. CONSTITUTION:A detection device for the ground of motor wires is equipped with a signal output circuit 46 which outputs signals based on the output from a polarity judging circuit 76 when a motor 20 is normally rotated, a signal output circuit 47 which outputs signals when the motor 20 is reversely rotated, and is also equipped with a signal output circuit 43 which outputs signals when PWM pulse signals driving the motor 20 are outputted. Terminal voltage VM1 is outputted with No.1 analogue switch 36 turned on when the motor 20 is normally rotated, meanwhile, terminal voltage VM2 is outputted with No.2 analogue switch 37 turned on when the motor 20 is reversely rotated so that the respective voltages are applied to the negative input terminal of a comparator 42 via a LPF 41. This thereby permits a ground detection signal to be outputted when the aforesaid input voltage is lower than a threshold voltage.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection device for a steering assist motor in an electric power steering device that assists steering force by the rotational output of a motor.

Conventional technology and its problems Mainly, the conventional electric power steering device is
The steering assist (auxiliary) motor is controlled based on the detected steering torque value and the detected vehicle speed value to generate steering assist torque.

However, if the motor drive circuit of an electric power steering device does not have a means to detect a motor line ground fault and power off the motor drive current, element damage or motor failure may occur when a motor line ground fault occurs. It will be connected.

Conventional motor line ground fault detection was performed in the same mode as overcurrent detection, as shown in FIG.

Figure 7 shows the assisted current feedback loop.
This figure shows an example of a drive circuit that drives the motor 20, and this drive circuit is a PWM (PulseνjdthModul) that follows the H-bridge drive method including four Swiss-Sochi circuits.
ation) The assist motor is driven and controlled by a forward and backward motion using pulses.

An assist current command is created based on the detected steering torque, detected vehicle speed, etc., and a control signal is created using a PWM modulation method based on this assist current command and the detected motor current fed back.

This control signal is applied to the drive circuit 30 of the steering assist motor 20 via the switch drive circuit 5.

The drive circuit 30 includes a so-called H-bridge circuit, and four switch circuits 30A to 30D are connected to the left and right arms. FIG. 7 shows the states of the switches when the motor 20 rotates in the normal direction, and in one cycle of the PWM carrier, the switch of the switch circuit 30A is in the on state (indicated by a circle), and the switch of the switch circuit 30B is in the on state.

Each switch of 30D is in the off state (indicated by an x mark)
The switch of the switch circuit 30C is kept on for a predetermined time period of the PWM carrier cycle (indicated by SW).

Therefore, when the main power switch 35 is on, current flows through the switch circuit 30A, the motor 20, and the switch circuit 30C for a predetermined period of time.

Resistors R and R2 are connected to the left and right arms of the H-brison in this drive circuit.

Based on the voltages dropped across the resistors R and R2, the motor current is detected at l and S. That is, the motor current detection circuit 8
0 includes two amplifier circuits 81 and 82 and an adder circuit 83, and a boosted voltage is obtained from a boosting power supply 85 that boosts the output voltage of the battery 32 from vBAT to a predetermined voltage. The voltage drops across resistors R and R2 are applied to amplifier circuits 81 and 81, respectively.
The signals are amplified at 82 and added at an adder circuit 83. The output of the adder circuit 83 is given to an overcurrent determination circuit 86. This circuit 8B detects an overcurrent when the output voltage of the adder circuit 83 exceeds a predetermined value (changeable according to the control signal), turns off the main power switch 35, and turns off the switch.
The operation of the Sochi drive circuit 5 is stopped.

In such a conventional circuit, an overcurrent occurs when a ground fault occurs in the motor wire, so the overcurrent determination circuit 86 detects the ground fault in the motor wire as well as the overcurrent detection.

However, in the conventional circuit shown in FIG. 7, a ground fault occurs on the cold side (ground side) of the motor wire.

Since it cannot be detected unless a reverse rotation command is given to the motor, there is a possibility that the motor will be controlled as is. In addition, the detection circuit includes a boost power source 8 as shown in FIG.
5 is required.

Furthermore, when the current detection resistors R and R2 are connected to the left arm and right arm of the H bridge, there is another problem in that it is difficult to adjust the variations in sensitivity of these resistors R and R2.

Summary of the Invention Purpose of the Invention This invention is capable of detecting ground faults in addition to overcurrent detection.
Moreover, it is an object of the present invention to provide a motor protection device that can detect ground faults not only on the hot side but also on the cold side, and does not require a resistor that requires adjustment as in the past.

Structure of the Invention 1 Operation and Effect The first invention includes means for creating an assist current command value based on detected steering torque, detected vehicle speed, etc., and four switching elements connected to the assist motor in an H-bridge type. , and depending on the magnitude of the deviation between the current command value and the detected motor current and the polarity of the current command value,
In an electric power steering device equipped with a motor drive device that controls the above-mentioned switching element using a pulse width modulation method, the terminal voltage at both ends of the assist motor is
A means for extracting a terminal voltage on the hot side according to the polarity, and a means for detecting a ground fault on the hot side of the assist motor by comparing the extracted terminal voltage with a predetermined threshold voltage. It is characterized by

According to the first invention, when a ground fault occurs on the hot side of the assist motor, the terminal voltage on the hot side becomes less than the threshold voltage, so that a ground fault on the hot side of the assist motor can be quickly detected. .

Since ground faults in motor wires can be detected separately from overcurrent detection, reliability is improved. Furthermore, since the step-up power supply required in conventional detection devices and the shunt resistor are also unnecessary, ground fault detection can be easily performed.

The second invention provides means for creating an assist current command value based on detected steering torque, detected vehicle speed, etc.
The motor is equipped with four switching elements connected in an H-bridge type, and the switching elements are pulsed depending on the magnitude of the deviation between the current command value and the detected motor current and the polarity of the current command value. In an electric power steering device equipped with a motor drive device controlled by a width modulation method, an assist ◆ means for extracting a hot side terminal voltage according to polarity among the terminal voltages at both ends of the motor, and a means for extracting a hot side terminal voltage according to the polarity, and every cycle.

The present invention is characterized by comprising means for detecting a ground fault on the hot side of the assist motor based on the presence or absence of the extracted hot side terminal voltage.

According to the second invention, when a ground fault occurs on the hot side of the assist motor, the terminal voltage on the hot side becomes zero, making it impossible to detect the terminal voltage on the hot side. This makes it possible to quickly detect faults. Moreover, the same effect as the first invention described above can be obtained.

A third invention provides means for creating an assist current command value based on detected steering torque, detected vehicle speed, and the like;
The motor is equipped with four switching elements connected in an H-bridge type, and the switching elements are pulsed depending on the magnitude of the deviation between the current command value and the detected motor current and the polarity of the current command value. In an electric power steering device including a motor drive device controlled by a width modulation method, means for detecting a current flowing through the assist motor, and when a control pulse is applied to the switching element by pulse width modulation, The present invention is characterized by comprising means for detecting a ground fault on the cold side of the assist motor based on whether the detected motor current is below a predetermined value.

According to the third invention, it is possible to detect a ground fault in the motor wire on the cold side, thereby improving its reliability.

According to the first to third inventions, the hot side of the assist motor;
Since ground faults in any of the motor wires on the cold side can be detected, element destruction and motor failure can be prevented when a motor wire ground fault occurs.

DESCRIPTION OF EMBODIMENTS FIG. 1 is a block diagram showing the entire control device included in an electric power steering device. FIG. 2 is a configuration diagram showing an example of a steering mechanical system to which this power steering device is applied.

First, the power steering mechanical system shown in FIG. 2 will be explained.

The rotational force of the steering handle 61 is transmitted through the handle shaft to a steering gear 62 including a pinion gear, and further transmitted to the rack shaft 64 by the pinion gear.
The wheel 65 is turned through the knuckle arm and the like. Further, the rotational force of the steering assist (auxiliary) motor (DC motor) 20 controlled and driven by the control device 10 is transmitted to the rack shaft 64 through the engagement between the steering mechanical system 63 including a pinion gear and the rack shaft 64, and is transmitted to the steering wheel. This will assist in steering by 6d. Handle 61 and motor 2
The rotational shaft of 0 is mechanically connected by gears 62, 63 and rack shaft 64. A steering torque sensor 21 detects steering torque (torsion torque).

Further, the vehicle speed is detected by the vehicle speed sensor 22, and the control device 10 controls the motor acceleration based on the detected torque, vehicle speed, etc., as described later. Control device 1
0 and the motor 20 are equipped with a battery 3 mounted on the vehicle.
Its operating power is supplied from 2.

As shown in FIG. 1, the control device IO includes a motor current detection circuit 15. A drive circuit 30 that drives the motor 20. CP 070. which controls the overall control of the motor 20; For example, it is composed of a microprocessor, a memory 19, an interface circuit between the computer, the above-mentioned person, an output device, etc. (not shown).

In FIG. 1, the steering torque detected by the steering torque sensor 2J is converted into a digital signal by an analog/digital (A/D) conversion circuit 11, and then input to the CPU 70. Further, the vehicle speed detected by the vehicle speed sensor 22 is counted by the counter 12, and a count value representing the vehicle speed is taken into the CPU 70. The CPU 13 creates an assist command based on the input steering torque and vehicle speed, and provides a control signal based on the command to the motor drive circuit 1 (l) as described later.

The motor 20 is driven by the motor drive circuit 30. The motor current is detected by a motor current detection circuit 15,
The signal is converted into a digital signal by the A/D conversion circuit 17 and taken into the CPU 70. This CPU 70 stores a memory 19 for storing desired data.

In FIG. 1, a motor line ground fault detection circuit, which will be described later, is omitted.

FIG. 3 shows an example of a motor line ground fault detection circuit.

The CPU 70 includes an assist command unit 71, and the assist command unit 71 creates an assist command value 3 based on the detected vehicle speed and detected torque manually inputted, and adds a viscosity compensation value and inertia compensation to this as necessary. A current command value ID is created by adding the values.

For example, the assist command value is determined according to the detected steering torque.
For a certain range of steering torque, the motor current is approximately proportional to the steering torque■. flows, and when the above range is exceeded, a certain constant motor current IM flows, and depending on the detected vehicle speed, when the vehicle speed is high, the motor current IN is decreased, and when the vehicle speed is slow, the motor current IN is increased. , is created to be able to control the motor 10.

Among the motor drive circuits 30, the switch circuit 30A.

The H-bridge connection configuration of 30D, 30B, and 30D is the same as that shown in FIG. The voltage VBAT of the battery 32 is applied to these switching elements via the main power switch 35. These switch circuits are controlled on and off by the switch drive circuit 5 based on control signals from the drive logic circuit 77, respectively, in a manner described later.

Although the functional blocks 4 71 to 78 inside the CPU 70 shown in FIG. 3 are actually realized by software (software servo), they are shown as a hardware configuration to make the explanation easier to understand. Some of these functional blocks 71 to 77 may be replaced with hardware circuits. The subtracter 72 calculates the current command value ID and the motor current I detected by the motor current detection circuit 15.
The deviation Id from that is calculated. This deviation ld is converted into an absolute value by an absolute value circuit 73 on the one hand, and its polarity (positive or negative) is determined by a polarity determining circuit 76 on the other hand. The output of the absolute value circuit 73 is compared with the triangular wave output from the PWM carrier frequency triangular wave generation circuit 74 in a voltage comparison circuit 75, and is output as a PWM pulse. This PWM pulse and the polarity discrimination result of the polarity discrimination circuit 76 are applied to a drive logic circuit 77, and from this circuit 77, a signal is generated to control the switching elements on and off in the following manner.

The output of the polarity discrimination circuit 76 is sent to the signal output circuits 46 and 47.
can be changed. Further, the PWM pulse is given to the signal output circuit 43.

5 Referring to FIG. 4, when rotating the motor 20 in the forward direction,
In one cycle T of the PWM carrier, the switch circuit 30
The switching element B is kept off, and the switching element of the switch circuit 30C is kept on. Then, the switching element of the switch circuit 30A takes a time T according to the deviation Id. 0, and other times (T-T)
Then it is turned off. Further, the switching element of the switch circuit 30D is turned off during the time T, and turned on during the other time period (TnT). In this way, the switch circuits 80A and 30D of the left arm n1 are reversed in on and off states and operate complementary.

Time T. . In this case, a current IM flows through the motor 20.

During reversal, in the PWM carrier period T.

The switching element of the switch circuit BOA is kept off, the switching element of the switch circuit 30D is kept on, and the switching elements of the right arm switch circuits BOB and 30C are controlled to be turned on and off in a complementary manner according to the time T. .

1 Let VMl be the voltage on the hot side of the motor 20 when the motor 20 rotates in the normal direction, and VM□ be the voltage on the hot side of the motor 20 when the motor 20 is rotating in the reverse direction.

The motor line ground fault detection device includes a signal output circuit 46 that outputs a signal when the motor 20 rotates in the normal direction based on the output from the polarity discrimination circuit 76. A signal output circuit 47 that outputs a signal when the motor 20 reverses, and a PW that drives the motor 20
A signal output circuit 43 is included that outputs a signal when the M pulse signal is output. The outputs of the signal output circuits 43 and 46 are sent to the first analog switch 36 via an AND gate 45, and the outputs of the signal output circuits 43 and 47 are sent to the second analog switch 37 via an AND gate 44, respectively. Given. This allows motor 2
When the motor 20 rotates in the normal direction, the first analog switch 3B turns on, and the terminal voltage VM1 passes through the low-pass filter 41, and when the motor 20 rotates in the reverse direction, the first analog switch 3B turns on.
7 is turned on, and the terminal voltage vM2 passes through the low-pass filter 4.
They are respectively applied to the negative input terminal of the comparator 42 via I.

7 A predetermined voltage generation circuit 4 is connected to the positive input terminal of the comparator 42.
The threshold voltage output from 8 is given. This threshold voltage is the PWM output from the gate drive circuit 5.
It is created to have a value that corresponds to the magnitude of the pulse signal.

The comparator 42 outputs a ground fault detection signal when the hot-side terminal voltage V or VH2 input manually via the low-pass filter 41 is below the old threshold voltage. When a ground fault occurs in the hot-side motor wire, the voltage V or VH2 becomes Ov, and a ground fault detection signal is output from the converter 1 42 and is applied to the hot-side motor wire ground fault detection circuit 50, which detects the ground fault in the motor wire. Detected.

When a ground fault in the motor line is detected, a power down signal is output from the ground fault detection circuit 50 and applied to the switch drive circuit 5 and the main power switch 35 of the motor drive circuit 30. This causes the switch drive circuit 5 to stop operating and the switch 35 to open. This makes it possible to prevent terminal damage and failure of the motor 20 due to motor line ground faults.

8. A detection resistor R for detecting the current flowing through the drive circuit is connected to the ground side of the motor drive circuit 30, and the motor current detection circuit 15 is connected to both ends of this detection resistor R.

The detected current □ of this detection circuit 15 is given to the subtracter 72 as described above, and the cold side ground fault detection section 78
given to. This cold side ground fault detection section 78 uses PWM
If the detected current IN is below a predetermined value while the pulse is being output, it is determined that there is a cold side ground fault. This predetermined value can also be changed depending on the width of the PWM pulse and the like. Upon detection of a cold-side ground fault, a power-down signal is output, and protection of the motor drive circuit is achieved in the same manner as described above.

FIG. 5 shows another embodiment. In this figure, the same parts as those shown in the ¥S3 figure are given the same reference numerals, and their explanation will be omitted. Furthermore, the CPU 70 is omitted in FIG.

The device shown in FIG. 5 has a signal output circuit 43.compared to the device shown in FIG. ANDGATE 44.45. A low-pass filter 41 and a comparator 42 are not provided. The output of the signal output circuit 46 is directly provided to the first analog switch 36, and the output of the signal output circuit 47 is directly provided to the second analog switch 37.

Also included is a watch dog timer 49, which includes a first . Second analog switch 36 or 37
A voltage vMl''M2 is input through the timer operation circuit.The timer operation circuit refreshes the timer 49 by the rising edge of the PWM pulse while it is being output.After the timer 49 is refreshed, the voltage signal ■ is input for a predetermined period of time or more.
If M1 or vM2 is not input, an output is generated, and the motor line ground fault detection circuit 50 determines that there is a hot side ground fault.

FIG. 6 is a flowchart showing the processing procedure for detecting a motor line ground fault by the CPU 70.

When the PWM pulse signal is output (YES in step 81), the rotation polarity of the motor is determined (step 8).
2). If the motor is rotating in the normal direction, the first analog switch 3B is closed and the motor terminal voltage "Ml" is set to the comparator 4.
2 or 0 to the timer 49, it is determined whether there is a ground fault in the hot side motor line (step 8L85). When the motor 2o is rotating in reverse, the second analog switch 37 is closed, thereby determining whether there is a ground fault in the hot side motor line (steps 84 and 85).

If it is determined that the hot side motor wire does not have a ground fault (
If NO in step 85), the presence or absence of a ground fault in the cold side motor wire is determined by the cold side ground fault detection section 78 (step 86). If a motor line ground fault is detected (step 85
or YES at 86), ground fault detection circuit 50 or CPU
A power down signal is output from 70, and the switch drive circuit 5 is stopped, and the main power switch 35 of the motor drive circuit 3o is turned off.

[Brief explanation of drawings]

Figure 1 is a block diagram of the control device included in the electric power steering device, and Figure 2 is a block diagram of the control device included in the electric power steering device.
FIG. 2 is a configuration diagram showing an example of a steering mechanical system. FIG. 3 shows an embodiment of the present invention, and is a circuit diagram of a motor 1 evening wire ground fault detection device, and FIG. 4 is a time chart showing the switching operation of the motor drive circuit. FIG. 5 is a circuit diagram showing another embodiment. FIG. 6 is a flowchart showing the procedure for detecting a motor line ground fault. FIG. 7 shows an example of a conventional motor line ground fault detection circuit. IO...control device. 15...Motor current detection circuit 30...Motor drive circuit. 36, 37...Analog switch. 42...Comparator. 46, 47...Signal output circuit. 49...Timer. 50...Ground fault detection circuit. 70...CPU. 71...Assist command unit. 76...Polarity discrimination circuit. 2 78... Cord side ground fault detection section. that's all

Claims (3)

[Claims] (1) Equipped with means for creating an assist current command value based on detected steering torque, detected vehicle speed, etc., and four switching elements connected to the assist motor in an H-bridge type, and detects the above current command value. In an electric power steering device equipped with a motor drive device that controls the switching element using a pulse width modulation method according to the magnitude of the deviation from the motor current and the polarity of the current command value, both ends of the assist motor A means for extracting the terminal voltage on the hot side according to the polarity among the terminal voltages of the assist motor, and detecting a ground fault on the hot side of the assist motor by comparing the extracted terminal voltage with a predetermined threshold voltage. A protection device for a motor in an electric power steering device, comprising means for protecting the motor. (2) A means for creating an assist current command value based on detected steering torque, detected vehicle speed, etc., and four switching elements connected to the assist motor in an H-bridge type, and detects the above current command value. In an electric power steering device equipped with a motor drive device that controls the switching element using a pulse width modulation method according to the magnitude of the deviation from the motor current and the polarity of the current command value, both ends of the assist motor means for extracting the hot side terminal voltage among the terminal voltages of the assist motor according to the polarity, and means for extracting the hot side terminal voltage of the assist motor based on the presence or absence of the extracted hot side terminal voltage for each cycle of the pulse width modulation. A protection device for a motor in an electric power steering device, comprising means for detecting a fault. (3) A means for creating an assist current command value based on detected steering torque, detected vehicle speed, etc., and four switching elements connected to the assist motor in an H-bridge type, In an electric power steering device including a motor drive device that controls the switching element using a pulse width modulation method according to the magnitude of the deviation from the detected motor current and the polarity of the current command value, the assist motor means for detecting a current flowing through the assist motor, and detecting a ground fault on the cold side of the assist motor based on whether the detected motor current is below a predetermined value when a control pulse is applied to the switching element by pulse width modulation. A protection device for a motor in an electric power steering device, comprising means for protecting the motor.